The easiest way to subtract several breaks is to do the calculation in minutes. Converting every break into a rounded decimal hour before subtraction can introduce small differences that add up across a week.
A session from 09:10 to 17:40 lasts 8 hours 30 minutes, or 510 minutes. Suppose you record a 35-minute lunch and two 10-minute unpaid breaks. Total break time is 55 minutes. Subtract 55 from 510 to get 455 minutes.
To express that as hours and minutes, divide 455 by 60: seven complete hours leave 35 minutes. The result is 7 hours 35 minutes. As a decimal it is approximately 7.5833 hours; rounded to two decimal places, 7.58.
Write down gross duration, each break, and net duration separately. If the final number looks wrong, you can check the inputs instead of repeating the whole calculation from memory. For multiple days, add the minute totals and round the combined decimal only when required.
Do not read 7.35 as seven hours and 35 minutes. In decimal hours, .35 represents 21 minutes. Also, do not subtract a break twice because it appears both in the timekeeping export and your handwritten notes.
This method calculates durations. It does not decide which breaks are paid, how overtime applies, or what rounding an employer requires. Apply those rules separately to the recorded result.